Injection-molding of plastic materials offers a relatively quick cycle time as compared to other plastic forming techniques such that the machine can often finish a run of a particular molded part in a comparatively short period of time. In order to change from molding one part to another, the mold base for the first part must be removed from the machine and a new mold base for the subsequent part installed. In view of the substantial cost of the machine, it cannot be allowed to sit idle. The time taken in changing the mold base must be kept to a minimum if the machine is to function productively. Currently, it takes from one to several hours to complete a mold base change.
In order to reduce the time required for the mold change process, attempts have been made to equip the platens of molding machines with an array of clamps and guides for supporting the mold base. For example, U.S. Pat. No. 4,500,274 issued to Cyriax et al discloses a quick-change mold assembly employing a plurality of spaced hydraulic clamps mounted on each platen of the press. Spaced guides are provided for receiving a plate attached to the back of a mold half. The clamps and guides are fastened directly to the platens. In order to add these parts to an existing machine, the press has to be disassembled so that the face of the platen can be drilled and tapped. There is no convenient way for machining the platen in the machine. After the platen is prepared, the clamps and guides are attached and the platen is reinstalled in the machine. This clearly involves a great expense which is limited to the particular machine. If the machine breaks or is down for service, the clamps and guides are not readily transferable to another machine.
FIG. 1 is a perspective view of a mold assembly 10 of the prior art secured to platens 22, 24 of an injection-molding machine. To attach the mold assembly 10 to the platens 22, 24, the mold assembly 10 is first lowered in between a stationary platen 22 and a moveable platen 24 by a hook 20 coupled to a crane or forklift (not shown). A crane or forklift is often required to lift the mold assembly 10 due to the weight of the mold assembly. An eyelet 18 secured to the mold assembly 10 provides a means to couple the mold assembly 10 to the crane or forklift. During the molding process, the movable platen 24 travels in a horizontal motion relative to the stationary platen 22 to open and close the mold assembly 10. Opening 28 on stationary platen 22 is sized to fit a locating ring (not shown). Tie bars 40 help to maintain proper alignment of the mold base halves.
The mold assembly 10 comprises a mold base 12 having two halves. The first and second halves of the mold base are separable along a parting line 26. The first mold base half includes a first mold clamping plate 14 secured thereto while the second mold base half includes a second mold clamping plate 16 secured thereto.
Clamping plate 14 is used to secure the first half of the mold base 12 to the moveable platen 24 and clamping plate 16 is used to secure the second half of the mold base 12 to the stationary platen 22. The clamping plates 14 and 16 are secured to platens 24 and 22 respectively using a plurality of clamps 30 and bolts 32.
FIG. 2 shows the plurality of clamps 30 and bolts 32 positioned at different angles around the periphery of the clamping plate 14. The installer installs the clamps 30 around the periphery of clamping plate 14 and tightens them in place using the bolts 32. Generally, the installer may use his or her own discretion and experience to determine the quantity and location of the clamps 30. This secures the clamping plate 14 to moveable platen 24. The installer secures clamping plate 16 to stationary platen 22 in similar fashion.
The clamp 30 is shown as having a generally rectangular shape with a slot formed in the clamp 30 to allow a bolt 32 to extend therethrough. As shown in FIG. 2A, the clamp 30 has a riser portion 30A that spaces clamp 30 approximately the thickness of clamping plate 14. The clamp 30 can be tightened in place by a bolt 32, such as a cap screw, to hold the clamp 30 and clamping plate 14 to the platen 24.
After the mold assembly 10 is secured to the platens 22 and 24, the hook 20 suspending the mold assembly 10 can be disconnected. The installer then connects the water lines and any necessary electrical connections.
The set-up time required to secure the mold assembly 10 to the platens 22 and 24 may be one to four hours. When this mold assembly is removed, it will take another one to four hours to install the next mold. This type of attachment method does not reduce the set-up time required for subsequent mold assembly insertions. This set-up time is costly in terms of machine utilization and the labor required.